Surface Composition and Surface Energetics of Various Eucalypt Pulps

In this paper we report on our study of the surface chemical composition, surface energy and acid-base characteristics of plantation eucalypt pulps obtained using the kraft, neutral sulphite semichemical (NSSC) and cold soda processes. X-ray photoelectron spectroscopy (XPS) was used to quantify the surface coverages of extractives and lignin. Inverse gas chromatography (IGC) was used to analyse the dispersive component and the acid-base characteristics of the pulp samples. The pulp yield and the total lignin and extractives in the pulp increased in the sequences of kraft, NSSC and cold soda. The relative surface concentrations of extractives and lignin on the pulps (expressed in terms of the ratios of the pulp surface coverage to the total content of these materials in the pulp) did not increase in the same sequence. The relative surface concentrations of lignin and extractives on the kraft pulps were found to be distinctively higher than those of the NSSC and cold soda pulps. The dispersive components of the surface energy of all pulps were similar before extraction, but increased by different degrees after extraction, with that of the cold soda pulp showing the lowest degree of increase. The acid-base characteristics of the pulps were evaluated using the method of acceptor and donor constants described by Schultz and Lavielle and the method of work of adhesion described by Lundqvist and Ödberg. A comparison of these methods has been made. The acidity of all pulps was found to increase after extraction. The degree of increase in pulp acidity is negatively correlated with the surface lignin concentration on the pulps. The low relative acidity of the cold soda pulp is probably associated with its high surface lignin coverage. An experimental model was established to test this hypothesis.